Sandwich structures of this type are known, for example, from French patent specifications No. 2.038.668 and 2.325.503, Swiss patent specification No. 394,566 European patent specification No. 281689 and from UK patent specifications No. 2138551 and 2263164.
The latter prior art reference discloses, inter alia, that the core may comprise an array of core units which are arranged in a staggered pattern such that in a first direction between said walls adjacent core units are substantially aligned and in a second direction between said walls which is transversal to said first direction at least some adjacent core units partly face each other.
Although the known core is suitable for many applications it has the drawback that its ability to conform to curvative in the said first direction is limited, and elongate gaps are present between adjacent rows of core units in order to create a drapeable core. These gaps form elongate zones where the walls are not supported. It has been found that in such elongate zones the walls may become subject to high stresses such that cracks in the walls or between walls and core may develop if the structure is heavily loaded in service. The risk of cracking appeared to be particularly high in areas where the gaps are relatively wide as may be the case if the structure comprises regions of compound curvature.